Field of the Invention
The invention relates to a fuel injection valve and a method for setting a predeterminable damping stroke of a fuel injection valve.
In a common rail injection system, before the main injection a preinjection (pilot injection) is made, in order to achieve gentler combustion in the combustion chamber of the internal combustion engine and thus reduce the noise output by the engine. The fuel quantity dispensed into the combustion chamber in the pilot injection is smaller than the fuel quantity in the main injection. In known fuel injection valves, the opening of the injection valve is delayed in order to attain small injection quantities.
From German Patent Disclosure DE 43 40 305 A1, a fuel injection valve is known in which during the valve opening, a defined volume is positively displaced into an annular chamber, and this volume is diverted via a throttle and the valve opening is thus delayed in a defined manner.
From Japanese Patent Disclosure 10122078 A, an injector is known in which a nozzle needle is axially displaceably disposed in the guide bore of a nozzle body and opens with a delay, after the valve opening, up to a predetermined damping stroke. On its upper end, the nozzle needle has a cylindrical shaft, which in turn is subdivided by a shoulder into an upper shaft part of larger diameter and a lower shaft part of smaller diameter. The shaft is disposed axially displaceably in the damping bore of a damping unit. If the deflection of the nozzle needle exceeds the damping stroke, then fuel flows out through the annular gap that is formed by the lower shaft part and the damping bore. The nozzle needle and the shaft are embodied in one piece, comprising a single body.